Wireless communications networks typically include one or more communications stations, generally called base stations, each communicating with its subscribers, also called mobile stations. Communication link from the mobile station to the base station is typically called uplink (UL) and communication link from the base station to the mobile station is typically called downlink (DL).
Cellular mobile communication networks use bidirectional communication between the base station and the mobile stations. It may be difficult to provide high data rates throughout a cell, particularly at the cell edge, due to factors such as wireless link degradation. One way to address this problem is reduction of the range of the cell, but it may lead to additional costs.
Relaying is generally considered as a method to ensure capacity improvement and coverage extension in cellular networks. Relaying technique is an ongoing topic in the 3GPP (third generation partnership project) LTE (long term evolution) standardization forum and the WiMAX (worldwide interoperability for microwave access) IEEE 802.16 (IEEE Standard for Local and Metropolitan Area Networks Part 16: Air interface for fixed and mobile broadband wireless access systems) standardization forum.
Relaying is realized through relay stations, such as fixed relay stations and/or mobile relay stations, between a base station and its mobile stations. The relay stations have an advantage in that they may not need the intelligence of the base station or connections to the backbone networks, yet still can contribute to the communication. The interpretation of several relay stations as a virtual antenna array allows the utilization of multiple input multiple output (MIMO) technology without requiring physical multiple antennas at a relay station (RS).
Communication link from the mobile station to the base station through the relay station is typically called uplink relay link (UL relay link) and communication link from the base station to the mobile station through the relay station is typically called downlink relay link (DL relay link).
Spatial multiplexing (SM) is a MIMO technique in which multiple data streams are transmitted at the same frequency but over different spatial channels. Space time block coding (STBC) is another MIMO technique in which multiple copies of one data stream are transmitted over a number of antennas. In STBC, a receiver combines the copies of the received signal in an optimal way to extract as much information as possible. Generally, SM requires a higher signal to noise ratio (SNR) for a successful receiving compared with STBC.
Cooperative relay may further enhance the performance of a relay-based system by treating the antennas of different relay stations (RS(s)) as a part of an antenna array, and applying the multi-antenna techniques among several RS(s). By properly coordinating the transmitted signals from several RS(s), a multi-antenna processing gain may be achieved, which may significantly improve the link quality, data rate and coverage of a relay-based system.
A cooperative hop-by-hop hybrid automatic retransmission request (HARQ) scheme is disclosed in an IEEE technical document “IEEE C802.16m-08/1279, Co-operative HARQ for IEEE802.16m: UL mode”. It proposes that the RS select a single RS to forward a data packet for the mobile station in a non-cooperative manner.